Highly purified human lung mast cells and peripheral blood basophils will be assessed for their content of the mediators of immediate hypersensitiviy and for their ability to generate and release these mediators after immunologic challenge. Dispersed lung cells will be prepared by tissue chopping and sequential digestion in proteases and collagenase and elastase. Mast cell separation will be done by sedimentation on a high-density metrizamide band followed by velocity sedimentation through a low-density metrizamide gradient. Basophils will be purified by sequential removal of other leukocyte types utilizing sedimentation methods, carbonyl iron phagocytosis, and adherence to siliconized glass beads. Cells will be sensitized with atopic sera and immunologically challenged with either specific antigen or absorbed anti-human IgE. Both released and intracellular mediators will be quantitated by bioassays and purified by standard methods. Pharmacologic modulation of mediator generation and release will be studied with concomitant measurements of cyclic nucleotides in the responsive cells. Guinea pig basophils and lung mast cells will be studied comparatively both with each other and with the human cells by analogous methods. Lastly experiments will be done to incorporate a 35S radiolabel into slow reacting substace of anaphylaxis. Successful radiolabeling would aid chemical definition of this mediator.